1. go to wikipedia
2. type chess into search bar
3. learn.
It started in India I heard...someone just said well some Rajas can be a man and these ones here can be less significant and someone else said wait a minute the universe is limitless it'd be impossible to play the kind of game I think you want to play...so let's confine your Rajas and less significant pieces in a grid of squares...that way the parameters are less daunting...but still quite challenging. Perfect for the human brain. White to move. Let's play!
Also the debate about in which country does not really matter, it was started on Planet Earth by a human being and its being played on Planet Earth by human beings.
The only variation in today's chess from the original chess, is en passant rule, no two step first moves for pawn, I am not sure about Castling but I think it was there.
how did chess start and how